The present invention relates to a process for the production of diaminodiphenylmethane and its higher homologues.
More specifically, the present invention relates to a process for the production of 2,2xe2x80x2,2,4xe2x80x2 and/or 4,4xe2x80x2-diaminodiphenylmethane and its higher homologous products.
Diaminodiphenylmethane (MDA) is an intermediate for the preparation of diphenylmethane diisocyanate (MDI) which, in turn, is a reagent for the production of polymers based on urethane/urea or epoxy resins. MDA is traditionally prepared from aniline, or from one of its derivatives, by reaction with formaldehyde in the presence of a concentrated solution of a strong acid such as, for example, hydrochloric, sulfuric or phosphoric acid. Literary sources which describe this type of synthesis are: J. Am. Chem. Soc. 57, 888, 1975; Chem. Tech., November 1984, 670; Kirk Othmer, Vol. II, 3rd Edition, 338-348.
The U.S. Pat. No. 5,241,119 describes a process for the preparation of 4,4xe2x80x2-diamino diphenylmethane which comprises the reaction between aniline and formaldehyde in the presence of a solid catalyst selected from zeolites, in particular Y zeolite, ZSM-5 zeolite or zeolites modified with one or more of the following metals: aluminum, boron, iron and titanium. The reaction is carried out in a solvent medium, at a temperature ranging from 50 to 200xc2x0 C., at a pressure depending on the boiling point of the solvent used.
The Applicant has now found that the preparation of 4,4xe2x80x2-diaminodiphenylmethane, optionally mixed with its 2,2xe2x80x2 and 2,4xe2x80x2 isomers, together with its higher homologues can be carried out with optimum results using as catalysts medium and large pore zeolites in acid form, partially or totally exchanged.
The object of the present invention therefore relates to a process for the preparation of diamino diphenyl methane, and its higher homologues having general formula (I): 
wherein "PHgr" represents a phenyl group, R represents a hydrogen atom or a C1-C8 (iso)alkyl, C4-C10 cycloalkyl or C6-C12 aromatic radical, and n is an integer greater than or equal to 1 and is such as to give a functionality ranging from 2 to 4, which comprises the re-arrangement reaction of the intermediate having general formula (II):
"PHgr"xe2x80x94NRxe2x80x94CH2xe2x80x94RNxe2x80x94"PHgr"xe2x80x83xe2x80x83(II)
in the presence of a zeolite in acid form having a spaciousness index ranging from 2.5 to 19, extremes included.
The spaciousness index is a parameter which provides the real pore width measurement of porous materials, such as zeolites. The spaciousness index is a parameter described in literature such as, for example, in U.S. Pat. No. 4,795,847 or in xe2x80x9cZeolites and Related Microporous Material: State of the Art 1994xe2x80x9d, Studies in Surface Science and Catalysis, vol. 84, 37, 1994, Elsevier Science B.V.; xe2x80x9cZeolite: Facts, Figures, Futurexe2x80x9d, 1989, 1115, Elsevier Science Publishers, B.V.
According to the present invention, preferred zeolites with a spaciousness index ranging from 2.5 to 19 are those consisting of synthetic crystalline material having the composition (III):
Mx/nn+[(AlO2)xe2x88x92x(SiO2)]xc2x7(H2O)pxe2x80x83xe2x80x83(III)
wherein x is less than 1, p is an integer greater than or equal to 1, generally ranging from 1 to 20, M is a metal of groups IA, IIA, or a lanthanide, n is the valence of M, and wherein M can be partially or totally exchanged with H+ or with the (NH4)+ ion or with an (NRxe2x80x24)+ cation with Rxe2x80x2 an alkyl radical, for example C1-C4, or an aryl radical.
Examples of zeolite which are included in general formula (III) and have a spaciousness index ranging from 2.5 to 19 are beta zeolite, mordenite, ZSM-12, MCM-22 and ERB-1. The beta zeolite described in U.S. Pat. No. 3,308,069 and having a spaciousness index of 19, is particularly preferred.
The zeolites used as catalysts in the process object of the present invention are preferably in acid form, i.e. in the form in which most of the cationic sites are occupied by hydrogen ions. They can be used as such or modified by the partial isomorphous substitution of aluminum with a metal selected from boron, iron or gallium or mixed with a ligand, for example alumina, and in the form of extruded pellets according to what is described in European patent 847,802.
The re-arrangement reaction takes place at a temperature ranging from 50 to 200xc2x0 C., preferably from 120 to 20 180xc2x0 C., in the presence of a solvent, selected from aliphatic or aromatic hydrocarbons or from halogenated aromatic hydrocarbons or aniline. Examples of particularly suitable solvents are aniline and chlorinated aromatic hydrocarbons such as m-dichlorobenzene and chlorobenzene.
The intermediate having general formula (II) is a product which is known in literature, in particular when R is equal to hydrogen (aminal). This intermediate can be obtained by the condensation of aniline, or a derivative of aniline wherein R is different from hydrogen, with formaldehyde, or a compound capable of producing formaldehyde under the reaction conditions. In particular, either formaldehyde in aqueous solution or formaldehyde in oligomeric form (trioxane), pre-dissolved in a solvent, can be used, with molar ratios aniline/formaldehyde ranging from 2 to 10, preferably from 3 to 5. At the end of the synthesis, the intermediate having formula (II) is separated with known techniques such as physical separation, distillation, etc. The product thus obtained can also be used with a water content less than or equal to 3% by weight, preferably less than or equal to 1.5%.
According to an alternative embodiment of the process for the preparation of diamino diphenyl methane having general formula (I), object of the present invention, the rearrangement reaction can be carried out by charging the zeolitic catalyst into a reaction mixture comprising aniline, or one of its derivatives, and formaldehyde, or a compound capable of producing formaldehyde under the reaction conditions. In this alternative case, it is preferable to operate with an excess of aniline, or its derivative, so that it contemporaneously acts as reagent and solvent. It has been observed, in fact, that by using an excess of reagent (aniline) instead of the traditional solvent, it is possible to vary the composition of the end-product, as can be noted from the enclosed examples.
The re-arrangement reaction according to the present invention can be carried out batchwise, in continuous or semi-continuous at atmospheric pressure or at a value which is such as to maintain the reactive system in liquid state.